AP Biology Origin of Life “…sparked by just the right combination of physical events & chemical processes…”

AP Biology BacteriaArchae- bacteria AnimaliaFungiProtistaPlantae Formation of earth Molten-hot surface of earth becomes cooler Oldest definite fossils of prokaryotes Appearance of oxygen in atmosphere Oldest definite fossils of eukaryotes First multicellular organisms Appearance of animals and land plants Colonization of land by animals Paleozoic Mesozoic Cenozoic Millions of years ago ARCHEAN PRECAMBRIAN PROTEROZOIC The evolutionary tree of life can be documented with evidence. The Origin of Life on Earth is another story… The evolutionary tree of life can be documented with evidence. The Origin of Life on Earth is another story…

AP Biology What is Life?  First we have to define LIFE…  organized as cells  respond to stimuli  regulate internal processes  homeostasis  use energy to grow  metabolism  develop  change & mature within lifetime  reproduce  heredity  DNA / RNA  adaptation & evolution

AP Biology Fossil Record  A. Provides evidence about the history of life on earth and shows how different groups of organisms have changed over time  B. Certain fossils are found only in rocks from a certain age  C. More than 99% of all the species that have ever lived are extinct

AP Biology  D. Most organisms die without leaving a fossil behind.  Most fossils form in sedimentary rock (sand, clay in river or lake beds) and are exposed and weathered by wind and heat  Many do not survive or are fragmented and not intact

AP Biology  E. Forces in the earth lift up and expose the rock layers containing the fossil, and paleontologists can date the fossil  F. Relative dating-the age of the fossil is determined by comparing in placement with that of other fossils in other layers  Index fossils (reference fossils) may be used

AP Biology  G. Radioactive dating uses the half-life of a radioactive form of an element to determine the age of the fossil  C-14: In nature there are several forms of carbon that have the same number of protons and electrons but a different number of neutrons. Matter (like an animal that makes a fossil) is a mixture of these forms, or isotopes. C-14 is radioactive, and decays into another isotope of carbon, C-12. The time it takes for half of the starting material’s C-14 to decay is called the half life. The other form of carbon, C- 12, does not decay. By comparing the amount of C-14 to the amount of C-12, scientists can calculate the age of the fossil

AP Biology

The Origin of Life is Hypothesis  Special Creation  Was life created by a supernatural or divine force?  not testable  Extraterrestrial Origin  Was the original source of organic (carbon) materials comets & meteorites striking early Earth?  testable  Spontaneous Abiotic Origin  Did life evolve spontaneously from inorganic molecules?  testable

AP Biology Conditions on early Earth  Reducing atmosphere  water vapor (H 2 O), CO 2, N 2, NO x, H 2, NH 3, CH 4, H 2 S  lots of available H & its electron  no free oxygen  Energy source  lightning, UV radiation, volcanic low O 2 = organic molecules do not breakdown as quickly What’s missing from that atmosphere?

AP Biology Water vapor Condensed liquid with complex, organic molecules Condenser Mixture of gases ("primitive atmosphere") Heated water ("ocean") Electrodes discharge sparks (lightning simulation) Water Origin of Organic Molecules  Abiotic synthesis  1920 Oparin & Haldane propose reducing atmosphere hypothesis  1953 Miller & Urey test hypothesis  formed organic compounds  amino acids  adenine CH 4 NH 3 H2H2

AP Biology Stanley Miller University of Chicago produced -amino acids -hydrocarbons -nitrogen bases -other organics It ’ s ALIVE!

AP Biology Bubbles … Tiny bubbles … Origin of Cells (Protobionts)  Bubbles  separate inside from outside  metabolism & reproduction

AP Biology Origin of Genetics  RNA is likely first genetic material  multi-functional  codes information  self-replicating molecule  makes inheritance possible  natural selection & evolution  enzyme functions  ribozymes  replication  regulatory molecule  transport molecule  tRNA & mRNA Dawn of natural selection

AP Biology Key Events in Origin of Life  Key events in evolutionary history of life on Earth  life originated 3.5–4.0 bya

AP Biology Prokaryotes  Prokaryotes dominated life on Earth from 3.5–2.0 bya 3.5 billion year old fossil of bacteria modern bacteria chains of one-celled cyanobacteria

AP Biology Oxygen atmosphere  Oxygen begins to accumulate 2.7 bya  reducing  oxidizing atmosphere  evidence in banded iron in rocks = rusting  makes aerobic respiration possible  photosynthetic bacteria (blue-green algae)

AP Biology First Eukaryotes  Development of internal membranes  create internal micro-environments  advantage: specialization = increase efficiency  natural selection! infolding of the plasma membrane DNA cell wall plasma membrane Prokaryotic cell Prokaryotic ancestor of eukaryotic cells Eukaryotic cell endoplasmic reticulum (ER) nuclear envelope nucleus plasma membrane ~2 bya

AP Biology Endosymbiosis Ancestral eukaryotic cell Eukaryotic cell with mitochondrion internal membrane system aerobic bacterium mitochondrion Endosymbiosis  Evolution of eukaryotes  origin of mitochondria  engulfed aerobic bacteria, but did not digest them  mutually beneficial relationship  natural selection!

AP Biology mitochondrion chloroplast Eukaryotic cell with chloroplast & mitochondrion Endosymbiosis photosynthetic bacterium Endosymbiosis  Evolution of eukaryotes  origin of chloroplasts  engulfed photosynthetic bacteria, but did not digest them  mutually beneficial relationship  natural selection! Eukaryotic cell with mitochondrion

AP Biology  Evidence  structural  mitochondria & chloroplasts resemble bacterial structure  genetic  mitochondria & chloroplasts have their own circular DNA, like bacteria  functional  mitochondria & chloroplasts move freely within the cell  mitochondria & chloroplasts reproduce independently from the cell Theory of Endosymbiosis Lynn Margulis